1. Field of the Invention
The present invention relates to the temperature control of at least one and preferably, multiple electrical Resistance heaters such as heaters at nozzles and hot runner molds at different zones, or areas where use of sensors is not feasible.
2. Description of the Prior Art
At present time, the control of multiple heaters is accomplished through the use of a heater, sensor and controller for each zone. The present control system can cost from $10,000 to $15,000 for controls and sensors for a complex mold.
Integral heater/sensor control systems for multiple heaters are further complicated by the need to calibrate to the resistance of each heater in the system. At present, calibration accuracy is dependent upon how accurately the resistance of the heaters can be controlled and duplicated from one unit to another unit at a reference temperature. Any resistance variation will result in a different process temperature for the same set point as one heater is substituted for another. To overcome this disadvantage, it is necessary to manufacture heaters with close tolerance of the base resistance which necessarily increases the cost of the heater.
The present invention overcomes the disadvantages of the prior art by providing an integral heater/sensor control system for multiple heaters of the type and material as later discussed in detail with variable base resistance, and also eliminates the individual temperature sensors for each heater and all of the associated wiring and connectors for each heater zone.